Presumably this is the last raw_spin_lock_irqsave() in force_qs_rnp(),the one right before the call to rcu_initiate_boost(). Could you pleaseverify for me?

If so, someone is holding the root rcu_node structure's lock for longerthan is good. Or that there is significant contention on that lock,which there might well be on large configurations. Any info on whois holding or contending for this lock would be very helpful!